This invention relates to a novel process for preparing benzophenone derivatives. Particularly, this invention relates to a novel process for preparing benzophenone derivatives useful as an intermediate in the preparation of anthraquinone dyes and colourless chromogenic compounds which form coloured markings upon contact with acidic materials by electron donor-acceptor colour-forming reaction. More particularly, this invention relates to a novel process for preparing benzophenone derivatives represented by the following general formula (I): ##STR1## wherein each of X and Y is hydrogen, halogen, nitro group, alkyl group, substituted alkyl group, amino group, substituted amino group, hydroxyl group, or substituted hydroxyl group; each of m and n is an integer of from 1 to 4.
There are known methods for preparing benzophenone derivatives represented by the general formula (I), for example U.S. Pat. No. 3,540,912 discloses a method in which the benzophenone derivatives are prepared by reacting aniline derivatives with substituted phthalic unhydrides in benzene with the use of Friedel-Crafts type catalysts. However, Friedel-Crafts reaction is prevented with the presence of water, because the catalysts are decomposed by water. Accordingly, it should be careful to handle the catalysts and it is necessary to use a dehydrated solvent and a complicated reactor which is completely protected from moisture. Additionally, since a large amount of isomers is produced because of the use of substituted phthalic acids, isolation is required to obtain the desired final product. This will result in reducing the yield of product.
An object of the invention is to provide a novel process for preparing benzophenone derivatives of a high purity in an extremely high yield.
Other objects and advantages of the invention will become apparent from the following description.